Apparatus and method of heat embossing thin, low density polethylene films

ABSTRACT

A method and apparatus for embossing plastic web materials, for instance, low density polyethylene film, have a movable, first embossing element having a plurality of male dies associated with a heat transferable member and a stationary, second embossing element having a plurality of female dies. The temperature of the heat transferable member is controllable so that the male dies can deform a range of deformable plastic materials. The stationary, second embossing element is alignable relative to the first embossing element and unheated so that the female dies are maintained at about ambient temperature during embossing.

FIELD OF THE INVENTION

[0001] The invention relates generally to the field of embossing. Moreparticularly, the invention concerns an apparatus and method ofembossing thin, low density polyethylene (LDPE) film using a temperaturecontrolled die and an opposing unheated die.

BACKGROUND OF THE INVENTION

[0002] Currently, radio frequency (RF) heating is the preferred industrytechnique for embossing thin film materials. In a typical RF process, asingle die is connected to a high voltage RF source. The film materialor web to be embossed is then arranged on a grounded metallic plate andpositioned for engaging contact by the single die. RF generates heat inthe web, directly or indirectly, which then softens the material to nearits melting point. With the associated pressure from the dies on thefilm material or web, a permanent impression of the intaglio on the diesis transferred to the web. A well-known shortcoming of the current RFtechnique is that it is extremely sensitive to the embossing material.In particular, film materials like polyethylene, have proven to be verypoor for absorbing RF energy. Moreover, the embossing process cycle timeusing RF is exceedingly long because of ineffectiveness of certainmaterials in absorbing RF energy. Further, another shortcoming ofpresent RF embossing techniques is that the quality of the embossedimage is not predictably consistent over a range of film materialproperties. This is particularly true with respect to embossing thin,low density polyethylene and similar film materials, such as polyesterand polystyrene.

[0003] U.S. Pat. No. 3,584,572 discloses a method and apparatus forsimultaneously heat stamping, embossing and cutting a workpiece, such asplastic sheet material, that uses a single die. However, a shortcomingof this development is that it uses a single die for cutting andembossing the film and the embossed image is formed only along an edgeof the workpiece.

[0004] Moreover, heretofore, embossed thermoplastic films such aspolyethylene, polypropylene, polybutene-1, polyvinyl chloride, and otherflexible thermoplastics normally extruded into film have been made byvarious methods. One method used to prepare embossed thermoplastic filmis to extrude the thermoplastic material, e.g., polyethylene, from aconventional slot extrusion die onto a continuously moving, smooth,cooled casting surface, e.g., a chill roll. The embossed films made bythe above described process often produce poor roll conformation, i.e.,have hard or soft spots, wrinkle or sag due to the inability todistribute zones of thickness variation across the width of the roll ofembossed film. Embossed film rolls of poor conformation producesproblems when running the film through fabricating machines or through afilm printing apparatus.

[0005] An example of a method and apparatus for producing film accordingto the foregoing slot die-chill cast roll technique is shown in U.S.Pat. No. 3,374,303.

[0006] Another technique used for embossing plastic film heretofore hasbeen the utilization of a heated engraved embossing roll used inconjunction with a backup roll. The resultant embossed film usually hasa very shallow and poorly defined pattern. An example of an apparatusand process for carrying out embossing of this type is shown in U.S.Pat. No. 3,176,058.

[0007] One of the drawbacks when using the heated drum or roll method toapply heat to the film prior to embossing is the difficulty in heatingthe film sufficiently so that it will take a deep, permanent embossedpattern which is a true reproduction of the engraved surface of theengraving roll.

[0008] Thus, it can be seen that the film embossing art is in need ofthe apparatus and method of the present invention whereby thermallydeformable plastic material, such as low density polyethylene can becontrollably heated to near its melting point and embossed, and thenquickly cooled to obtain a density depression in the plastic webmaterial forming a deep, permanent embossed pattern on the material.Moreover, the invention enables wide variation in control of theparameters which will permit variation in the physical properties of theembossed material, i.e., modulus, surface gloss, embossed pattern depth,tensile strength, and impact strength.

SUMMARY OF THE INVENTION

[0009] It is, therefore, an object of the invention to provide a methodof embossing that is more effective than present techniques.

[0010] Another object of the invention is to provide a method ofembossing that utilizes a pair of dies using a controlled heat source tocontrol the heat generated in the plastic material.

[0011] The present invention is directed to overcoming one or more ofthe problems set forth above. Briefly summarized, according to oneaspect of the present invention, an apparatus for embossing indicia on aplastic web material comprises:

[0012] a rigid upright frame;

[0013] a source of power associated with said frame;

[0014] a first, movable embossing element mounted for movement on saidframe, said first embossing element comprising a heat transferablemember heated by said source of power, a mounting plate member having afirst side and a second side, said first side being affixed to said heattransferable member, and a plurality of male dies affixed to said secondside of said mounting plate member, each one of said plurality of maledies having an intaglio design thereon; and

[0015] a second, stationary embossing element supportably alignable insaid frame with said first embossing element, said second embossingelement comprising a plurality of female dies each one of which toreceive a corresponding one of said plurality of male dies, one of saidplurality of female dies having a corresponding intaglio design thereonand a mounting plate for supporting said plurality of female dies.

[0016] In another aspect of the invention, a method of embossingthermally deformable plastic web material comprising the steps of:

[0017] (a) providing an embossing unit comprising a first, movableembossing element having a heat transferable member, a mounting platemember supported affixed to said heat transferable member and aplurality of first dies having a predetermined male pattern affixed tosaid mounting plate member; and a cooperating, second embossing elementalignable with said first embossing element, said second embossingelement having a plurality of second dies having a predetermined femalepattern for receiving said predetermined male pattern of said firstdies, and, a support plate for supporting said plurality of second dies;

[0018] (b) providing power to said heat transferable member, said heattransferable member heated to a predetermined temperature;

[0019] (c) arranging said thermally deformable plastic web material onsaid plurality of dies;

[0020] (d) moving the first embossing element towards said secondembossing element so that said plurality of first dies engageablycontact said thermally deformable plastic web material;

[0021] (e) maintaining said plurality of first dies in contact with saidthermally deformable plastic web material for a predetermined period oftime thereby forming an embossed image on said thermally deformableplastic web material corresponding to said predetermined male andfemales patterns on said plurality of first dies and said plurality ofsecond dies; and,

[0022] (f) moving the first, movable embossing element away from thethermally deformable plastic web material so as to permit cooling of thethermally deformable plastic web material.

[0023] The present invention has the following advantages: the embossedimage has a predictably high quality; the process enables multiple logosto be produced on a single web; the processing time is much shorter; theprocess is effective for a range of materials, particularlypolyethylene; and it is easier to operate in a production.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other objects, features, and advantages of thepresent invention will become more apparent when taken in conjunctionwith the following description and drawings wherein identical referencenumerals have been used, where possible, to designate identical featuresthat are common to the figures, and wherein:

[0025]FIG. 1 is a perspective view of embossing unit with dies separatedapart;

[0026]FIG. 2 is a cross-section view of the embossing unit showing diescompressed about a web to be embossed;

[0027]FIG. 3 is a top plan view of the top die; and,

[0028]FIG. 4 is a top plan view of the bottom die.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Turning now to the drawings, and more particularly to FIGS. 1 and2, apparatus 10 of the invention is illustrated. Broadly defined,apparatus 10 for embossing plastic web material 1, such as thin, lowdensity polyethylene film (LDPE), has a pair of opposing embossingelements 14, 22 (described below) arranged in a rigid upright frame 12and a source of power 15 conveniently associated with frame 12 foractivating associated components (described below). A plurality of maledies 20 in first embossing element 14 is controllably heated by a heattransferable member 16. Opposing female dies 24 in second embossingelement 22 remain at ambient room temperature throughout the embossingprocess. Through an air cylinder the heated male dies 20 are presseddown on plastic web material 1 toward bottom, female dies 24. Theplastic web material 1 arranged between top, male dies 20 and bottom,female dies 24 undergoes an embossing process under the righttemperature and the pressure. After the top, male dies 20 are removedfrom the plastic web material 1, embossed indicia, e.g., logos, remainpermanently impressed in the plastic web material 1. Using this process,we surprisingly found that the quality of the embossed impression ispredictably consistent compared with prior art methods. Referring toFIG. 1, more particularly, first, movable embossing element 14 ismounted for vertical movement on frame 12. Skilled artisans willappreciate that vertical movement of embossing element 14 may beachieved by any number of conventional means, such as, by a screw drivemechanism, belt drive mechanism or chain drive mechanism. Importantly,first embossing element 14 has a heat transferable member 16, preferablymade of metallic alloy material, heated by the source of power 15. Thoseskilled in the art will appreciate that heat transferable member 16 maybe made of other thermally conductive materials, such as aluminum andaluminum alloy. These materials are known to have favorable thermalconductivity suitable for embossing. In the preferred embodiment, heattransferable member 16 is mounted to a mounting plate member 18 having afirst side (not shown) and similar second side (not shown). First sideis structurally attached to heat transferable member 16 while aplurality of male dies 20 are affixed to the second side of the mountingplate member 18. Hence, mounting plate member 18 provides means ofassociating the male dies 20 to the heat transferable member 16. Thoseskilled in the art of embossing will appreciate that the male dies 20and corresponding female dies 24 (described below) have some sort ofpredetermined intaglio design thereon for embossing the plastic webmaterial 1.

[0030] Referring again to FIG. 1, a second, stationary embossing element22 is arranged for translational and rotational movement about base 28on frame 12. In a preferred embodiment, second embossing element 22 isalignable relative to the first embossing element 14 by translationaland rotational movements on base 28. Alignment of second embossingelement 22 is important because the plastic web material 1 can be easilyarranged on the second embossing element 22 and then positioned foralignment with first embossing element 14 for embossing. Since secondembossing member 22 is stationary relative to first embossing element14, second embossing element 22 is fixed in a plane against verticalmovement on frame 12 relative to first embossing element 14. Moreparticularly, second embossing element 22 comprises the plurality offemale dies 24, designed to receive a corresponding one of the pluralityof the male dies 20, and die support plate 26. Skilled artisans willappreciate that each of the female dies 24 have corresponding intagliodesign thereon and a support plate for supporting said plurality offemale dies 24.

[0031] Referring to FIG. 1, apparatus 10 further comprises means forcontrolling the position of the first embossing element 14 relative tothe stationary, second embossing element 22. While skilled artisans willappreciate that several means of controlling the position of firstembossing element 14 may be used with substantially similar results, weprefer using a stopping switch 13 cooperatively associated with thetravel path of movable first embossing element 14. Thus, when firstembossing element 14 contacts the stopping switch 13, further movementof the first embossing element 14 is interrupted until the stoppingswitch 13 is either deactivated or the force exerted by the firstembossing member 14 on the stopping switch 13 is removed.

[0032] Depicted in FIG. 1, heat transferable member 16 has a temperaturecontrolling means, preferably a thermocouple 30, operably associatedwith the source of power 15. An important advantage of temperaturecontrolling means is that it enables materials having a range of meltingtemperatures to be embossed using the apparatus 10 of the invention.Moreover, a means, preferably a timer, for controlling the heating timeof the heat transferable member 16 is provided. This assures that theplastic web material 1 will sufficiently deform while under controlledheat thereby enabling an embossed image to be impressed on the plasticweb material 1.

[0033] An important feature of the apparatus 10 of the invention is thatsecond embossing element 22 is unheated and maintains a temperatureequal to about ambient temperature while the first embossing element 14is controllably heated. Because there is no heat source in the secondembossing element 22 the surface texture of the plastic web material 1(LDPE) exposed to the male dies 20 will not be changed after embossing.Thus, we have shown that the invention generates sharp logo imagesbecause of this embossing configuration.

[0034] In another embodiment of the invention, a method of embossingthermally deformable plastic web material, such as thin, low densitypolyethylene film, comprises the step of providing an apparatus 10 forembossing as described above. Power is then provided to the heattransferable member such that the heat transferable member is heated toa predetermined temperature. The material to be embossed, typically athermally deformable plastic web material is then arranged on the femaledies. The first embossing element comprising the male dies is then movedinto engaging contact with the thermally deformable plastic webmaterial. A stop switch restricting the vertical movement of firstembossing element keeps the dies in appropriate position for apredetermined period of time. Thus, an embossed image is formed on thethermally deformable plastic web material corresponding to thepredetermined male and female patterns on the male and female dies.After the embossed impression is made on the deformable plasticmaterial, the first, movable embossing element is moved away from thethermally deformable plastic web material so as to permit cooling of thethermally deformable plastic web material.

[0035] The invention has been described with reference to a preferredembodiment. However, it will be appreciated that variations andmodifications can be effected by a person of ordinary skill in the artwithout departing from the scope of the invention. PARTS LIST:  1 filmor plastic web material 10 apparatus 12 frame 13 stopping switch 14first embossing element 15 source of power 16 heat transferable member18 mounting plate member 20 male dies 22 second embossing element 24female dies 26 die support plate 28 base of apparatus 10 30 thermocouple

What is claimed is:
 1. Apparatus for embossing plastic web material,said apparatus comprising: a rigid upright frame; a source of powerassociated with said frame; a first, movable embossing element mountedfor movement on said frame, said first embossing element comprising aheat transferable member heated by said source of power, a mountingplate member having a first side and a second side, said first sidebeing affixed to said heat transferable member, and a plurality of maledies affixed to said second side of said mounting plate member, each oneof said plurality of male dies having an intaglio design thereon; and asecond, stationary embossing element supportably alignable in said framewith said first embossing element, said second embossing elementcomprising a plurality of female dies each one of which to receive acorresponding one of said plurality of male dies, each one of saidplurality of female dies having a corresponding intaglio design thereonand a mounting plate for supporting said plurality of female dies. 2.The apparatus recited in claim 1 further comprising means forcontrolling the position of said first embossing element relative tosaid stationary second embossing element, said means comprising astopping switch fixed cooperatively associated with said movable firstembossing element.
 3. The apparatus recited in claim 1 furthercomprising means for controlling the temperature of said heattransferable member, said means comprising a thermocouple operablyconnected to said source of power.
 4. The apparatus recited in claim 1further comprising a means for controlling the heating time of said heattransferable member, said means for controlling comprising a timer. 5.The apparatus recited in claim 1 wherein said second embossing elementis maintained at about ambient room temperature.
 6. A method ofembossing thermally deformable plastic web material comprising the stepsof: (a) providing an embossing unit comprising a first, movableembossing element having a heat transferable member, a mounting platemember supportedly affixed to said heat transferable member and aplurality of first dies having a predetermined male pattern affixed tosaid mounting plate member; and a cooperating, second embossing elementalignable with said first embossing element, said second embossingelement having a plurality of second dies having a predetermined femalepattern for receiving said predetermined male pattern of said firstdies, and, a support plate for supporting said plurality of second dies;(b) providing power to said heat transferable member, said heattransferable member heated to a predetermined temperature; (c) arrangingsaid thermally deformable plastic web material on said plurality ofsecond dies; (d) moving the first embossing element towards said secondembossing element so that said plurality of first dies engageablycontact said thermally deformable plastic web material; (e) maintainingsaid plurality of first dies in contact with said thermally deformableplastic web material for a predetermined period of time thereby formingan embossed image on said thermally deformable plastic web materialcorresponding to said predetermined male and female patterns on saidplurality of first and said plurality of second dies; and, (f) movingthe first, movable embossing element away from the thermally deformableplastic web material so as to permit cooling of the thermally deformableplastic web material.
 7. The method recited in claim 6 furthercomprising the step of adjustably controlling the heating temperature ofsaid plurality of first dies so as to deform said thermally deformableplastic web material.
 8. The method recited in claim 6 furthercomprising the step of adjustably controlling the heating time of saidheat transferable member.
 9. The method recited in claim 6 furthercomprising the step of adjustably controlling the position of saidplurality of fist dies relative to said female dies.
 10. A method ofembossing thin, low-density polyethylene films, comprising the steps of:(a) providing an embossing unit comprising a first, movable embossingelement having a heat transferable member, a mounting member supportedlyaffixed to said heat transferable member and a plurality of first dieshaving a predetermined male pattern affixed to said mounting platemember; and a cooperating, second embossing element alignable with saidfirst embossing element, said second embossing element having aplurality of second dies having a predetermined female pattern forreceiving said predetermined male pattern of said plurality of firstdies, and, a support plate for supporting said plurality of second dies;(b) providing power to said heat transferable member, said heattransferable member heated to a predetermined temperature; (c) arrangingsaid thin, low density polyethylene film on said plurality of seconddies; (d) moving said first embossing element towards said secondembossing element so that said plurality of first dies engageablycontact said thin, low density polyethylene film; (e) maintaining saidplurality of first dies in contact with said low density polyethylenefilm for a predetermined period of time thereby forming an embossedimage on said thin, low density polyethylene film corresponding to saidpredetermined male and female patterns on said plurality of first diesand said plurality of second dies; and, (f) moving the first, movableembossing element away from the thin, low density polyethylene film soas to permit cooling of the film.